Patent GB-1235102-A (GB)
Title: Vehicle transmission and control systems
Inventor: WRIGHT JAMES
IPC: F16H59/54
Filed: 1967-06-03
Abstract: 1,235,102. Controlling industrial trucks. ELECTRO - HYDRAULICS Ltd. 23 Aug., 1968 [3 June, 1967], No. 25735/67. Heading B7H. [Also in Divisions B8, F2 and H2] In a vehicle transmission and control system (see Division F2) vehicle wheels A, B are each driven by a fixed displacement hydrostatic motor C, D supplied by a swash plate pump 1 the displacement of which is varied by a doubleacting hydraulic jack 2 having a lost motion connection 2A with the pump swash plate. The boost pump 5 supplies the hydraulic circuits L, M through non-return valve H, J and solenoid valves 8, 9, 10 and 11 through non-return valves 48, 49 excess pressure being relieved through valve K. In their de-energized state valves 8, 9 supply pressure to both sides of jack 2 and valves 10, 11 are closed. The pump 1 may be a D.C. motor or an A.C. motor driven from the battery through an inverter or an I.C. engine. Electric/hydraulic circuit.-In an application to a fork lift truck the carriage lift and mast tilt are supplied by an electric motor 6, Figs. 2A, 2B, 2C, 2D. Forward or reverse travel and swash plate tilt are controlled by pedals 12, 13 spring biased into a neutral position and acting on a pivoted plate 14 which is connected to a wiper arm 16 which contacts sectors 17, 18 of a code pattern 19A pivoted coaxially with the wiper arm 16 and moving with jack 2. A further sector 20 is engaged by either of two brushes 21, 22. The lift motor 6 cannot be energized until key switch 24 is operated and the operator is seated to operate a seat switch 23. The release of band brakes on motors C, D operates a switch 25 to allow motor 3 to be energized and application of the foot brake causes a switch 26 to be operated to cause the transmission to return to neutral and the motor 3 to be cut off from the battery 4. Printed circuit switches 27, 28 are operated by the carriage lift and mast tilt control levers 57, 58. Truck parked.-The switches and contactors are as shown in Figs. 2A, 2B, 2C, 2D. Operation.-When the operator is seated and the key switch turned "on" switches 23, 24 are operated. Selective control of the carriage lift or mast tilt levers 57, 58 to direct fluid to appropriate jacks causes brush 27A or 28A to bridge strips 27B, 27C or 28B, 28C, 28D to complete a circuit closing reed switch 56 which closes a circuit through the operating coil of the lift contactor 34 to energize the lift motor 6. The latter drives pump 7 to supply liquid to the selected service. A resistor 73 and condenser 74 arranged across the operating coil of the reed switch maintained current flow for 3 to 5 seconds after the opening of the switches to permit continued energization of the lift motor whilst other services are energized. A diode 75 prevents excessive arcing due to induced voltage. Forward travel.-Movement of pedal 12 to select forward travel moves wiper arm 16 clockwise on to sector 17 thereby completing circuits which energize the operating coils of reed switches 50, 54 which in turn energize the solenoid valve 8 and the operating coil of the drive motor contactor 39. Simultaneously with the making of the latter circuit a further circuit is made which assists the magnetic bias of switch 55 which retains it in the closed condition. Drive motor 3 drives pumps 1 and 5 and as pressure builds up it is delivered through solenoid valve 9 to the annular area side of jack 2 forcing out liquid from the opposite full area side to reservoir E. The jack 2 tilts the swash plate to increase pump delivery and code pattern 19A is likewise rotated until sector 20 is engaged by brush 21. A holding circuit is completed through the second operating coil of reed switch 54 to keep the drive contactor made and the operating coil of switch 55 which acts against the magnetic bias also simultaneously energized, the magnetic bias retaining the switch contacts closed. Simultaneously a positive feed from battery 4 is supplied to the operating coils of reed switches 51 and 53 but the circuits are not completed unless any one of the following control operations are effected. Travel forwards steady speed.-With pedal 12 depressed code pattern 19A rotates until sector 17 disengages from wiper arm 16 to break the operating coil circuit of reed switch 50 thereby de-energizing the solenoid valve 8. The circuit of the first operating coil of the reed switch 54 is also broken but since the second operating coil remains energized the contacts of switch 54 remain closed. A diode 117 suppresses arcs at switch 50. Non-return valves 48, 49 maintain jack 2 hydraulically locked. Travel forwards up gradient.-When a gradient increase causes increased current demand from motor 3 the contacts of switch 77 are operated at a predetermined value to break the circuit of the operating coil of reed switch 50 thus preventing energization of the solenoid valve 8 and any increase in pump swash angle. At a limiting current value a circuit is completed through the coil of reed switch 51 which completes a circuit to energize the solenoid valve 9 so that jack 2 moves to reduce the swash plate angle and hence the pump delivery. The truck decelerates and battery demand is reduced. At the appropriate lower levels of current the current detector 44 returns switches 77 and 120 to their unoperated state so that the truck can be accelerated forwards from the speed to which it has been reduced. Return to neutral from steady speed forward.- When pedal 12 is released the wiper arm 16 engages sector 18 since code pattern 19 is still rotated clockwise. The operating coil of reed switch 51 is energized via the unoperated switch 77, diode 133, and through sector 18 and wiper arm 16. Operation of switch 51 energizes the solenoid valve 9 and the annular area side of jack 2 is connected back to the tank and the resulting movement of the jack causes the code pattern 19A to rotate anticlockwise until sector 18 leaves the wiper arm 16 causing switch 51 to de-energize the solenoid valve 9. The first operating coil of reed switch 54 which was deenergized when switch 51 is operated is deenergized when the sector 20 leaves the wiper arm 16. The sector 20 also leaves the brush 21 causing de-energization of the second operating coil of the reed switch 54 whose contacts open after a short delay whilst condenser 118 discharges through resistor 119. On opening switch 54 the operating coil of the contactor 39 is broken causing disconnection of the battery 4 from drive motor 3. The two operating coils of the reed switch 55 are also de-energized respectively when the sector 20 leaves brush 21 and when contactor 39 breaks. The transmission is now in neutral. Reed switches 54, 55 are protected from arcing by a diode 92A. Surge suppression for the operating coils of switches 54, 55 is provided by diodes 61A, 94A, 103A, condenser 118 and resistor 119. Acceleration in reverse.-Depression of selector pedal 13 rotates the wiper arm 16 anti-clockwise to engage the sector 18 and energize the operating coil of reed switch 51 permitting the jack to extend. The first operating coil of the reed switch 54 is also energized and the switch 54 closes completing the circuit through switch 55 to energize the operating coil of the drive contactor which connects the battery 4 to the drive motor 3. Anti-clockwise rotation of code pattern 19A causes engagement of sector 20 with brush 22 to complete a holding circuit through the second operating coil of switch 54 to maintain contactor 39 made. A circuit is also completed through the first operating coil of switch 55 to hold the contact closed. Reverse travel at steady speed.-When the code pattern 19A has rotated so that sector 18 leaves wiper arm 16 the operating coil of the reed switch 51 and the solenoid of valve 9 are deenergized to lock jack 2 into the position into which it has moved. The drive contactor is maintained by the circuit through the reed switch 54. Reverse travel up gradient.-The circuit through current detector 44 controls solenoids 8, 9 in a manner similar to that described for travel forwards up gradient. Braking.-When the handbrake is applied the switch 25 is returned to the position shown in Fig. 2B and if the truck is travelling forward the operating coil of reed switch 53 is energized or if in reverse the operating coil of reed switch 52 is energized which respectively complete circuits energizing solenoid valves 10 or 11. This provides a parallel path for liquid being returned from the jack 2 to the reservoir E to return jack 2 to its neutral position more rapidly. Alternatively the solenoid valves 10, 11 are energized by application of foot brake 26 which also isolates the return path to the battery 4 from the wiper arm 16 to prevent any selection of forward or reverse travel by foot pedals 12 or 13. In an alternative method of braking a proportional opening valve is connected by non-return valves to each side of the jack 2 and to the reservoir E and conductor 116 omitted. Opening of this valve returns the swash plate to the neutral position at a speed proportional to the amount of opening of the valve. In a modification which prevents the transmission starting up under load when control fuse 67 is replaced following its previous failure whilst the truck is in motion, an accumulator T and non-return valve U are connecnected to conduit G. When the control fuse 67 is replaced (switches 23, 24, 25 being in the operated state and switch 26 unoperated) switch 50 or 51 will operate to cause energization of solenoid valve 8 or 9. This connects one or other side of the jack 2 to the reservoir E enabling the accumulator T to discharge into the opposite side to return jack 2 to the midposition. Control currents are minimized by power amplification using reed switches 50 to 56 or alternatively transistorized circuits can be used. In a further embodiment the displacement of hydrostatic motors C, Fig. 3, is reduced when the displacement of the pu